1. Field of the Invention
The present invention relates to a highly reliable photosensor and a method of manufacturing the photosensor with ease.
2. Description of the Prior Art
Conventionally, silicon photodiode type linear photosensor arrays are generally known in the art as photoelectric conversion means which constitute a readout section of, for example, a facsimile apparatus or a copier. This type of linear photosensor is difficult to manufacture in an elongated form due to the limits in the size of a monocrystal available. Therefore, it is necessary to optically scale down an original to be optically scanned, thereby resulting in a disadvantage in miniaturizing the apparatus.
Apart from the above, extensive development in the technology for making elongated and large-scale photosensors has been made recently using film forming methods, such as glow discharge method, sputtering method, ion plating method, and vacuum evaporation method, or a method for coating a mixture of binding resin and semiconductor material.
A planar type photoconductive photosensor may be given as one example of photosensors constituting an elongated line sensor, in which a pair of metal electrodes are formed on a photoconductive layer, such as chalcogenide, CdS, CdS-Se, and amorphous silicon (hereinafter referred to as a-Si), the pair of metal electrodes being disposed on the photoconductive layer facing each other so as to form a gap serving as a light reception portion.
One example of the structures of conventional photoconductive photosensors is shown in FIG. 1. The structure includes a substrate 11, photoconductive layer 12 with non-doped impurities, ohmic contact layer 13, conductive layers 14-1, 14-2 serving as electrodes, light reception portion 15, and protective layer 16 of SiNH.
With this structure of conventional photosensors, a glow discharge device is required for forming a passivation film. In addition, film forming processes take a long time. Therefore, productivity is low. Moreover, since a substrate must be subjected to heating for a long time for forming an SiNH film, heat hysteresis may become one of The causes of inconsistent sensor characteristics.